Reinforcing strips for corrugated paperboard and related method and apparatus for its manufacture

ABSTRACT

Reinforcing packaging strips comprised of low melt point, low density polyethylene coated on at least one surface of a substrate. Corrugated paperboard packaging comprising a fluted paperboard medium having in selected areas a reinforcing liner, wherein said reinforcing liner has an adhesive surface which when heat activated adheres to the medium surface. The resulting structure has high strength and tear resistance in designated areas.

This application claims the benefit of U.S. provisional application No.60/230,671 filed Sep. 7, 2000, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the field of packaging, specificallycorrugated paperboard packaging. In particular, the invention providesreinforcing strips for corrugated paperboard structures and the relatedmethod and apparatus for manufacture.

BACKGROUND OF THE INVENTION

Corrugated paperboard is currently used in countless packagingapplications and is, by far, the most popular packaging for articles ormaterials suitable for packaging in boxes, whether for shipment, storageor both. Because of commercial value, the conventional corrugatedpaperboard container has been the focus of extensive research anddevelopment resulting in continuous improvements therein. Of late, mucheffort has been put into developing containers with improved stackingstrength as well as deriving more strength from less fiber mass.

Of particular interest herein is the fact that loads and stresses placedon corrugated packages are rarely distributed uniformly. This can be dueto many different reasons; uneven weight distribution of packagecontents, shape of package contents, handling (or mishandling), etc.Whatever the cause, the result is often loads and stresses that arehighly concentrated or localized. Industry has sometimes addressed thisissue by improving package design, often times quite creatively.However, good design and engineering practices dictate that a package bemanufactured to perform in a “worst case” scenario, so the inevitableresult is a package which meets the stringent performance requirementsof certain areas while providing excessive packaging in others.Importantly, this results in a package that is not as economical or costeffective as it could be.

For example, one of the most critical performance criteria for manycorrugated paperboard boxes is stacking strength. Box designerstypically increase stacking strength by increasing the weight of theliners and/or medium. This provides the added stacking strength neededin the walls of the box, but also provides additional strength (andfiber mass) in the top and bottom of the box where it is not needed,unnecessarily increasing cost.

Another example involves packages that need to be bulge and/or burstresistant due to outward force applied by the package contents, often afluid material. Like the stacking strength example supra, a commonremedy to this problem is simply making a box out of heavier components.This remedy may solve the problem, but is uneconomical. A commonpost-manufacturing remedy to this problem consists of simply applying areinforcing tape, such as a nylon mesh reinforcing tape, to the externalsurface of a package. This remedy is cumbersome, costly due to the laborinvolved, often provides sub-optimum performance, typically not anoption if aesthetics are an issue, and adds little to prevent packagedeformation. Methods are available wherein a reinforcing mesh and orstrands are included between the medium and outside liner, but theseremedies provide reinforcement to the entire package, including areaswhere reinforcement is unnecessary.

Yet another example involves packages which include closure flaps thatare subject to repeated opening and closing. These packages often failat the closure scoreline. A common remedy is to apply reinforcing tapealong the scoreline. As with the bulge resistant example above, thisremedy is cumbersome, costly due to the labor involved, often providessub-optimum performance, and is typically not an option if aestheticsare an issue.

A final example involves large appliances packaged in regular slottedcontainers with a basiloid flap at the upper end. In this application,lift trucks fixed with a flat, laterally situated lifting hook, lift andmove these loaded containers by inserting the flat hook into the spacebetween the container sidewall and basiloid flap then lifting the entirepackage by the flap. This method of transport places highly localizedloads on the basiloid flap/joint area and has resulted in failure withinthe joint, specifically along lateral scorelines. This problem has beenremedied by either applying reinforcing tape around the joint area orincreasing the basis weight of the components in the container. Theformer requires additional labor and provides sub-optimum performance,while the latter unacceptably increases packaging costs.

Many technologies and methods are known that enable the manufacture ofreinforced packages, specifically reinforced corrugated paperboardpackages, but each have limitations which fall short of the benefitsprovided by this invention.

U.S. Pat. No. 4,398,650 to Holmes et. al. discloses a corrugatedcontainer wherein a plurality of reinforcing strands are containedbetween the medium and outside liner. The enhancement provided by thismethod is limited to bulge and burst resistance. It adds little in termsof stacking strength, rigidity or scoreline integrity.

U.S. Pat. No. 5,285,957 to Halsell discloses a reinforced corrugatedcontainer wherein a reinforcing mesh composed of natural cellulosicstrands is contained between the medium and outside liner. As with theHolmes patent listed above, the enhancement provided by this disclosureis limited to bulge and burst resistance. This method provides noadditional stacking strength, rigidity or scoreline integrity, and isnot selectively applied.

U.S. Pat. No. 4,437,850 to Ono discloses a process of manufacturingreinforced corrugated cardboard type containers wherein a reinforcingagent is applied along longitudinal scorelines between the outside linerand medium. In this disclosure, the lines of reinforcing agent arelocated such that they cover the areas that are scored and ultimatelybecome the upper and lower horizontal perimeter of a finished box. Asdisclosed, this method enhances stacking strength by minimizing crushfailure in the vicinity of the treated scorelines, but adds no stackingstrength to the walls or additional resistance to bulge or burst. Mastimportantly, this method requires that scoring, folding and formingoccur before the reinforcing agent hardens.

U.S. Pat. No. 3,411,689 to Brackett discloses placing narrow strips ofthermoplastic material into corrugated board flutes at intervals andbefore the corrugated medium is attached to a second liner.

U.S. Pat. No. 3,796,307 to McKinney discloses a heat shrinkablepolymeric film attached to corrugated fluting, the resulting product isformed into a carton or bundled package and then the entire package isheated to shrink the polymeric film.

U.S. Pat. No. 4,936,451 to Shuert is directed to a container comprisedof a sleeve and end unit. The sleeve is made of corrugated material andcontains a plurality of slots which interlock with latches on the endunit.

Canadian Pat. No. 889808 to Karass discloses a “weftless” tape or strapproduct. The tape is comprised of threads of synthetic resin, includingpolyethylene. An adhesive is then applied to the threads.

U.S. Pat. No. 3,406,052 to Mendham is directed to waterproof containersthat maintain strength. This is accomplished by passing corrugatedfiberboards through heat-softened films of thermoplastic material(including polyethylene) and then applying a certain amount of pressureto adhere the films to the faces of the fiberboard. The edges of thecoated fiberboards are crushed and then sealed with a waterproofsubstance.

U.S. Pat. Nos. 4,095,692 and 4,177,895 both to Shelton are directed to acontainer having walls laminated with polymeric film, includingpolyethylene. The purpose of the lamination or “shroud’ of polymericfilm is to prevent air current from passing through the interior of thecontainer.

The present invention is an improvement over prior art processes byproviding reinforcing packaging strips to strengthen the load-carryingjoints in corrugated packaging by selectively applying the strips todesired areas. Further, in addition to increasing strength, the stripsprovide more tear resistance to the reinforced joint and stiffen theentire flap, enabling it to carry a heavier load without failing.

Typically, corrugated paperboard is manufactured such that the finishedproduct includes two opposed liners, a fluted medium disposed in betweenwith adhesive forming permanent bonds between the flute tips and theopposed liners. Corrugated paperboard that includes two liners about onemedium is typically called single wall. The term double wall typicallydescribes three liners and two mediums in alternating layers, whiletriple wall refers to alternating layers including four liners and threemediums.

In general, to manufacture single wall corrugated paperboard, threesubstrates are used, a singleface liner, a doubleface liner, and acorrugating medium, and several manufacturing steps are followed. First,a continuous web of corrugating medium is directed between twocorrugating rolls that form the medium into a corrugated web withlateral flutes. Next, the fluted medium is directed against aglue-bearing cylinder that places a metered amount of adhesive on eachflute tip of one side.

The medium is then directed against a continuous web of singleface linersuch that the glue-bearing flute tips bond evenly to the liner to form asubstrate commonly called singleface-corrugated paperboard. Thesingleface-corrugated paperboard is then directed against a secondglue-bearing roll that places a metered amount of adhesive on the flutetips located opposite the singleface liner which is then directedagainst a continuous web of double-face liner such that the glue-bearingflute tips bond evenly to the doubleface liner to form single wallcorrugated paperboard (commonly referred to as combined board).

The next step in the manufacturing process involves moving the web ofcombined board through a controlled hot plate section in order to heatand cure the adhesive. Upon exiting the hot plate section, the webtravels through a cooling section wherein ambient air cools thepaperboard and adhesive. The web is then directed through aslitter/knife section wherein the combined board is continuously slitlongitudinally, then laterally cut into sheets suitable for convertinginto boxes or other finished containers. Double and triple wallcombinations are manufactured in the same general way except that two orthree layers of single-face corrugated are directed together along witha doubleface liner. The steps involved in manufacturing corrugatedpaperboard are highly standardized throughout the packaging industry andwell known within the art. However, these known processes are notentirely satisfactory in certain applications such as in strengtheningload-carrying joints in corrugated packaging and enhancing tearresistance to movable joints in corrugated packaging.

The invention disclosed herein addresses the problems discussed aboveand the shortcomings of currently available remedies. A general objectof the present invention is to provide reinforcing strips made of apaper substrate coated on one side with a low melt, low densitypolyethylene for application to selected portions of corrugatedpaperboard structures.

Another object of the invention is to provide a method for manufacturingreinforced corrugated paperboard packaging that is more economical overthe prior art method of reinforcing which uses nylon-based tape.

A further object of the invention is to provide a method formanufacturing reinforced corrugated paperboard packaging whereinreinforcement can easily be applied only to select areas.

A specific object of the invention is to provide an apparatus formanufacturing selectively reinforced corrugated paperboard.

Another specific object of the invention is to provide a method formanufacturing selectively reinforced corrugated paperboard that iscompatible with existing manufacturing equipment and requires nomodification of major equipment.

Another object of the invention is to provide a method for manufacturingselectively reinforced corrugated paperboard that utilizes aheat-activated adhesive that is activated by ambient heat present in aconventional hot plate section.

A further object of the invention is to provide a method formanufacturing selectively reinforced corrugated paperboard that remainsformable and pliable after manufacturing.

Another further object of the invention is to provide a strongercorrugated box structure by stiffening the folding flap with reinforcingstrips.

SUMMARY OF THE INVENTION

In the present invention, these purposes, as well as others which willbe apparent, are achieved generally by reinforcing packaging stripscomprised of low melt, low density polyethylene coated on a papersubstrate and the related method and apparatus for producing such. Thesereinforcing strips are used in the manufacture of corrugated paperboardstructures to strengthen the load-carrying joints in the resultingstructure and to provide tear resistance to the reinforced joint. Thesestrips, selectively placed on the structure, also reinforce flaps thatare subject to repeated folding as well as stiffen the entire flap andbody of the structure enabling it to carry a heavier load withoutfailing. These strips are a significant improvement over the nylon meshreinforced tape of the prior art and provide the resulting paperboardstructure with good stacking, uniform distribution of loads and stressand bulge and/or burst resistant properties.

In a preferred embodiment, the polyethylene coated strip is placed sothat it reinforces the score on the corrugated board that eventuallyforms the joint at the top of the box, thus selectively reinforcing theclosure scoreline to permit repeated opening and closing withoutfailure.

Other objects, features and advantages of the present invention will beapparent when the detailed description of the preferred embodiment ofthe invention are considered with reference to the drawings which shouldbe construed in an illustrative and not limiting sense as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a web of singleface corrugatedpaperboard, bottom liner, and reinforcing liner as it is combined priorto entering the hot plate section of a typical corrugator;

FIG. 2A is a longitudinal cutaway view of conventional finished singlewall corrugated paperboard;

FIG. 2B is a longitudinal cutaway view of finished single wallcorrugated paperboard including a reinforcing liner;

FIG. 3A is a longitudinal cutaway view of finished double wallcorrugated paperboard;

FIG. 3B is a longitudinal cutaway view of finished double wallcorrugated paperboard including a reinforcing liner;

FIG. 4 is a layered top view of a finished sheet of reinforced singlewall corrugated paperboard showing each component layer;

FIG. 5 is a top view of a scored and cut blank prior to being folded andglued to form a regular slotted style corrugated container;

FIG. 6A is a top view of the scored and cut blanks which make up aninterlocking double cover style corrugated container.

FIG. 6B shows the blanks prior to being folded, glue, stapled andgenerally erected;

FIG. 7A is a top view of a scored and cut blank prior to being foldedand glued to form a regular slotted container with basiloid flap;

FIG. 7B is a perspective view of a regular slotted style container withbasiloid flap;

FIG. 8 is a longitudinal cutaway view showing the detail of the basiloidflap;

FIG. 9 is a diagram illustrating how the reinforcing strip is introducedon the corrugator (overhead view);

FIG. 10 is a diagram illustrating how the reinforcing strip isintroduced on the corrugator (side view);

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the invention, reinforcing packaging strips comprisedof a heat activated adhesive, preferably a low melt point, low densitypolyethylene, coated on at least one surface of a paper substrate areprovided. In alternate embodiments, both sides of the paper substratemay be coated with the heat activated adhesive.

Also provided is a reinforced corrugated paperboard substrate suitablefor the manufacture of packaging, comprising a top paperboard linerincluding a top and bottom surface; a fluted paperboard medium includinga top and bottom surface, wherein the flute tips of the top surface ofsaid medium are adhered to the bottom surface of said top liner; areinforcing liner including a top and bottom surface, wherein the topsurface of said reinforcing liner is adhered to the bottom flute tips ofsaid medium, said reinforcing liner having a width less than the widthof said medium; an adhesive covering the bottom surface of saidreinforcing liner; and a bottom paperboard liner including a top surfaceand a bottom surface, the top surface of said bottom liner being adheredto the bottom surface of said reinforcing liner by means of saidadhesive therebetween.

The adhesive is a heat activated compound activated by ambient heatpresent in the hot plate section of the corrugator. Preferably, theheat-activated adhesive is a thermoplastic material with a melting pointbelow 250° F. The term “thermoplastic” as used herein refers to plasticmaterials, known to one of ordinary skill in the art, which are fusibleand rendered soft and moldable by heat. Most preferable thethermoplastic material used in the invention is a low-densitypolyethylene resin. Typically, the low-density polyethylene resin has acoating weight in the range of 5.0-20.0 lbs./3000 sq. ft. and a densityin the range of 0.90-1.00 g./cm³.

In alternate embodiments the heat-activated adhesive is a thermosettingmaterial with a melting point below 250° F. The term “thermosetting” asused herein refers to plastic materials, known to one of ordinary skillin the art, that are rendered hard by heat.

The invention also provides a method of manufacturing reinforcedcorrugated paperboard comprising the steps of (i) providing a continuousweb of corrugated paperboard; (ii) feeding a reinforcing linercomprising a heat activated adhesive coated on at least one surface of apaper substrate over selective areas of said corrugated paperboard toform a laminated structure; (iii) heating said laminated structure to atemperature high enough to melt said heat activated adhesive causingsaid liner to adhere to the corrugated paperboard in the selected areas.

The invention also provides an apparatus for manufacturing reinforcedcorrugated paperboard comprising (i) first supply means for providing acontinuous web of corrugated paperboard; (ii) second supply means forproviding a reinforcing liner having an adhesive coating on at least onesurface; (iii) placement means for placing said reinforcing liner onselective areas of said corrugated paperboard; and (iv) means foradhering said liner to said selective areas of the paperboard. In apreferred embodiment of the apparatus the means is a hot plate.

The details of the invention are further illustrated by reference to thedrawings. In particular, FIG. 1 illustrates the doublebacker nip,hotplate, and cooling sections of a conventional corrugator. Themanufacturing process prior to this point is highly standardizedthroughout the industry, is well known within the art. A web ofsingleface corrugated paperboard, comprised of singleface liner 1 andcorrugated medium 2, enter the doublebacker nip 6 of a conventionalcorrugator. The flute tips of medium 2 each carry a metered amount ofadhesive that spans the entire web of each flute. A continuous web ofdoubleface liner 3 simultaneously enters the nip where it is pressedinto contact with the flute tips of the corrugated medium 2 at nip point6 located between pressure roll 7 and hotplate belt drive roll 8. Thepressure at nip point 6 is adjustable.

The invention process provides a continuous web of reinforcing liner 4pre-coated on the bottom side with heat activated adhesive 5,correspondingly fed into the nip point between the singleface anddoubleface webs. The lateral placement and width of reinforcing liner 4is adjustable. The lineal velocities of the three webs entering the nippoint are controlled to be equal. After passing through nip point 6, thecombined board 11, comprised of single face liner 1, corrugated medium2, doubleface liner 3, reinforcing liner 4, and heat activated adhesive5, then enters the hot plate section 9 wherein it slides across the topsurface of each of a series of hot plates. The number of plates in a hotplate section is typically machine specific. The temperature of each hotplate is controlled, and the surface temperature is typically heldbetween 290-350° F. As the combined board passes through the hot platesection, ambient heat activates adhesive 5 causing it to melt. Uponexiting the hot plate section, the combined board 11 passes through acooling section wherein the temperature of adhesive 5 falls belowmelting point, allowing adhesive 5 to solidify and form an adhesive bondbetween doubleface liner 3 and reinforcing liner 4. After exiting thecooling section 10, combined board 11 is longitudinally slit and orscored, then laterally cut into sheets of various sizes. In separatemanufacturing operations, said sheets are then cut and scored to formblanks which are then folded and/or glued into finished containers.

FIG. 2A shows a longitudinal cutaway of a conventional finished piece ofsingle wall corrugated paperboard comprised of singleface liner 1,corrugated medium 2, and doubleface liner 3. The flute tips are bondedto each liner by means of a starch-based adhesive. The manufacturingprocess involved in making the typical combined board of FIG. 2A is wellknown within the art. FIG. 2B shows a longitudinal cutaway of a finishedpiece of reinforced single wall corrugated paperboard according to theinvention comprised of singleface liner 1, corrugated medium 2,reinforcing liner 4, heat activated adhesive 5, and doubleface liner 3.Heat activated adhesive 5 forms a continuous bond between the entiresurface of reinforcing liner 4 and corresponding surface of doublefaceliner 3. Under normal operating conditions, the bond formed by heatactivated adhesive 5 is stronger than the starch bond between eithersingleface liner 1 and medium 2 or reinforcing liner 4 and medium 2 suchthat the overall resistance of the structure to separating under opposedforces (indicated by force vectors A and B) is not diminished.

In a preferred embodiment, heat activated adhesive 5 is a low meltingpoint, low density polyethylene resin applied to the bottom surface ofreinforcing liner 4 by means of extrusion coating processes wherein amachine width web of liner is coated, then slit down to the desiredwidth. Field tests show that polyethylene resins with densities in therange of 0.915-1.000 g/cm³, melting points in the range of 220-225° F.,melt indices in the range of 8.5-12.0 g/10 min., and coating weights upto 20 lbs./3000 sq. ft. meet performance criteria. Extrusion coating andslitting processes are well known within the art and common to theindustry.

FIGS. 3A and 3B illustrate the prior art and the invention,respectively, and are longitudinal cutaway views of finished double wallcorrugated paperboard.

FIG. 4 shows a finished piece of combined board separated to show eachindividual component including singleface liner 1, corrugating medium 2,doubleface liner 3, reinforcing liner 4, and heat activated adhesive 5.FIGS. 7A and 7B further illustrate a feature of the preferred embodimentof subject invention wherein reinforcing liner 4 is located about ascoreline 21. As previously noted, the lateral position(s) and width(s)of reinforcing liner(s) 4 are adjustable.

FIG. 5 shows a preferred embodiment of the subject invention, wherein ablank for a regular slotted style container includes a reinforcing liner4 as represented by the hatched area, a glue tab 12 and top and bottomflaps 13-20. Score lines are indicated by dashed lines 21. Reinforcingliner 4 is disposed between doubleface liner 3 and corrugating medium 2.In the embodiment shown in FIG. 5, the width of the reinforcing liner 4spans the entire height of the walls of a regular slotted container,thus providing increased overall stacking strength as well as increasedburst resistance throughout each vertical wall, without needlesslyadding fiber and costs to the top and bottom flaps.

FIG. 6A shows a blank for the body including glue tab 22, locking flaps23-30 and scorelines indicated by dashed lines 21, and typical blank forthe top and bottom covers including scorelines 21 and closure flaps31-34. Importantly, the body blank shown in FIG. 6A includes reinforcingliners 4 located across the top and bottom horizontal scorelines 21.FIGS. 6A and 6B illustrate a preferred embodiment of the subjectinvention wherein reinforcing liner 4 is located about the top andbottom horizontal scorelines 21 to add strength to each closure flaparea. Interlocking double cover style containers are often used tocontain heavy appliances and are normally moved about by clamp trucksthat clamp only the joint areas. Thus, placing the reinforced strips inthese selective areas provide the package with enhanced tear andstrength properties.

FIG. 7B illustrates a regular slotted container with basiloid flap. FIG.7A shows a top view of a blank including glue tab 45, side walls 47-50,top flaps 37-40, bottom flaps 41-44, scorelines 21, reinforcing linerrepresented by hatched area 4, and basiloid flap walls 35 and 36. Asindicated by FIG. 8, upon folding and gluing, walls 35 and 36 form ahorizontal flap substantially parallel to sidewall 47. Steel band 46 isplaced tightly about the upper perimeter of the container and issituated around sidewalls 47-50, around basiloid flap wall 35, andbetween flaps 35 and 36. The basiloid flap structure enables lifting andmoving of the container by a mechanism that includes a flat plate-likemember inserted between sidewall 47 and flap wall 35. In thisembodiment, reinforcing liner 4 is positioned to reinforce the scorelinebetween flap walls 35 and sidewall 47 to prevent failure during liftingand moving.

The process and apparatus for making the reinforcing strips forcorrugated paperboard packaging are shown in FIGS. 9 and 10. Inparticular, FIGS. 9 and 10 illustrate the present process, where rollsof linerboard are coated on one side with a heat activated adhesive,preferably, a low melt point, low density adhesive polyethylene resinstrip, slit to size and rewound into smaller rolls. These rolls ofpre-coated reinforcing liner are mounted on a roll stand with a feedermechanism. The roll stand/feeder mechanism feeds the strips into thecorrugator just after the doublebacker and immediately before the hotplate section.

The roll stand holds two rolls of the polyethylene coated paper at onetime and permits splicing from one roll to another. The roll standcontains hoists to lift the polyethylene coated rolls into place and hasa pneumatic breaking system to control unwinding speed. The roll standis portable which allows it to be moved out of the way when not in useand the extending feeding mechanism enables it to be set upperpendicular to the corrugator.

In a preferred embodiment, the polyethylene coated strip is placed sothat it reinforces the score on the corrugated board that eventuallyforms the joint at the top of the box. The polyethylene coated strip isplaced on the inside of the combined corrugated board, between thecorrugating medium and doubleface liner (also referred to as adoubleback liner). As stated above, the roll stand/feeder mechanismfeeds the strips into the corrugator just after the doublebacker andimmediately before the hot plate section. The heat from the hot platesection of the apparatus melts the polyethylene causing the polyethylenecoated liner to bond with the doubleface liner. A starch-based adhesiveapplied to the flute tips of the corrugating medium in the doublefaceliner bonds the polyethylene coated strip to the corrugating medium.

The size of the strip used can be varied depending on the application,from narrow widths that reinforce small areas of the container to largerstrips that can reinforce entire panels. In a preferred embodiment ofthe invention, six-inch wide strips are used.

As shown in FIG. 10, the polyethylene coated liner 60 is feed from theroll stand feeder mechanism to the corrugator between a continuous webof single faced liner with medium 70, and double back liner 80. The rollstand/feeder mechanism feeds the strips into the corrugator just afterthe doublebacker and immediately before the hot plate section. The heatfrom the hot plate section of the apparatus (collectively 90) melts thepolyethylene causing the coated liner to bond with the doubleface liner.

The present invention described herein by referring to drawings ofexamples of how the invention can be made and used. In these drawings,reference characters are used throughout the views to indicate like orcorresponding parts. The embodiments shown and described herein areexemplary. Many details are well known in the art, and as such areneither shown nor described. Even though numerous characteristics andadvantages of the present invention have been described in the drawingsand accompanying text, the description is illustrative only, andmodifications may be made in the detail, especially in matters of shape,size, and arrangement of the parts, within the principles of theinventions, to the full extent indicated by the broad general meaning ofthe terms used in the attached claims.

The invention now being fully described, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

1. Reinforcing packaging strips comprised of low melt point, low densitypolyethylene coated on at least one surface of a paper substrate.
 2. Areinforced corrugated paperboard substrate suitable for the manufactureof packaging, comprising: a top paperboard liner including a top andbottom surface; a fluted paperboard medium including a top and bottomsurface, wherein the flute tips of the top surface of said medium areadhered to the bottom surface of said top liner; a reinforcing linerincluding a top and bottom surface, wherein the top surface of saidreinforcing liner is adhered to the bottom flute tips of said medium,said reinforcing liner having a width less than the width of saidmedium; an adhesive covering the bottom surface of said reinforcingliner; and a bottom paperboard liner including a top and bottom surface,top surface of said bottom liner adhered to bottom surface of saidreinforcing liner by means of said adhesive therebetween.
 3. Thereinforced corrugated paperboard substrate according to claim 2, whereinsaid adhesive is a heat activated compound activated by ambient heatpresent in the hot plate section.
 4. The reinforced corrugatedpaperboard substrate according to claim 3, wherein said heat-activatedadhesive is a thermoplastic material with a melting point below 250° F.5. The reinforced corrugated paperboard substrate according to claim 4,wherein said thermoplastic material is a low-density polyethylene resin.6. The reinforced corrugated paperboard substrate according to claim 5,wherein said low-density polyethylene resin has a coating weight in therange of 5.0-20.0 lbs./3000 sq. ft.
 7. The reinforced corrugatedpaperboard substrate according to claim 5, wherein said low-densitypolyethylene resin has a density in the range of 0.90-1.00 g./cm³. 8.The reinforced corrugated paperboard substrate according to claim 3,wherein said heat-activated adhesive is a thermosetting material with amelting point below 250° F.
 9. A method of manufacturing reinforcedcorrugated paperboard comprising the steps of: providing a continuousweb of corrugated paperboard; feeding a reinforcing liner comprising aheat activated adhesive coated on at least one surface of a papersubstrate over selective areas of said corrugated paperboard to form alaminated structure; heating said laminated structure to a temperaturehigh enough to melt said heat activated adhesive causing said liner toadhere to the corrugated paperboard in the selected areas.
 10. Themethod according to claim 9, wherein said heat activated adhesive is athermoplastic material with a melting point below 250° F.
 11. The methodaccording to claim 10, wherein said thermoplastic material is alow-density polyethylene resin.
 12. The method according to claim 11,wherein the said low-density polyethylene resin has a coating weight inthe range of 5.0-20 lbs./3000 sq. ft.
 13. The method according to claim10, wherein the said low-density polyethylene resin has a density in therange of 0.90-1.00 g./cm³.
 14. The method of claim 9, wherein said heatactivated adhesive is a thermosetting material with a melting pointbelow 250° F.
 15. An apparatus for manufacturing reinforced corrugatedpaperboard comprising: first supply means for providing a continuous webof corrugated paperboard; second supply means for providing a linerhaving an adhesive coating on at least one surface, placement means forplacing said liner on selective areas of said paperboard; reinforcingmeans for adhering said liner to said selective areas of the paperboard.16. The apparatus according to claim wherein said reinforcing means is ahot plate.